Regenerating of casting sand

ABSTRACT

Spent contaminant-coated casting sand is admixed with fresh uncontaminated casting sand, and the thus-obtained mixture is subjected to mechanical agitation, during which the fresh sand scours the contaminant coating off the spent sand and thus regenerates the sand.

United States Patent 1191 Jacob Dec. 31, 1974 REGENERATING 0F CASTING SAND [56] References Cited [76] Inventor: Hermann Jacob, Fachenfelder Weg UNITED STATES PATENTS 115, 2092 Horst, Germany 1,587,621 6/1926 Walther 106/389 Filed y 2 1973 2,813,318 11/1957 Horth 24l/40X [21] Appl. No.: 376,004 Primary Examiner-Donald G. Kelly Attorney, Agent, or Firm-Michael S. Striker [30] J l 1201:3915: Apglication Priority Data 2233] [57] ABSTRACT u y 'ermany H Spent contaminant-coated casting sand is admixed with fresh uncontaminated casting sand, and the thus- [52] 51/8 obtained mixture is subjected to mechanical agitation, [51] Int Cl 824C 1/00 824C 3/12 B02: 19'/o6 during which the fresh sand scours the contaminant [58] Field oi s 851m 24l/DIG. 10 5 1s 26 mating Spent Sand and regenerates sand.

8 Claims, 1 Drawing Figure REGENERATING OF CASTING SAND BACKGROUND or THE INVENTION The present invention is concerned with the regeneration of spent casting sand, and more particularly with a method and an apparatus for effecting such regeneration.

Casting sand or molding sand is used for making forms or molds in which metallic objects can be cast. The casting sand is admixed with binding materials, for instance sodium silicate or, more recently, synthetic plastic resin binders, in order to make it hold together in the desired shape.

It is, of course, economically desirable that the sand be recovered once the mold used for casting of a particular item is no longer required. This of course means that the sand must be regenerated, that is the spent sand must be freed of the coating of binder and other contaminants which forms on each grain of sand during the molding operation, since this coating of burnt binder and possible other contaminants would prevent proper r'e-use of the sand. This regeneration of the sand can be carried out by heating the sand sufficiently to burn off the contaminant coating, orby treating the sand chemically to dissolve the coating. Both of these methods are, however, relatively time-consuming and certainly too expensive to be economically feasible.

For this reason the currently almost exclusively used regenerating method for such sand involves entraining the spent casting sand in a stream of air which is directed against a stationary obstacle. The impacting of the thusentrained sand on the obstacle results in a mechanical agitation of the entrainedsand, so that the individual sand grains rub against one another during this agitation and tea certain extent scour off the contaminant coating.

Apparatus used for this purpose works well if the contaminant coating is relatively brittle and can therefore be readily removed by scouring, that is by impacts or the like. In such instances it is assumed as a general rule that approximately 80 percent of the thusregenerated spent sand can be re-used, and that percent must be discarded, this 20 percent being predominantly composed of scoured-off or broken-off contaminant coating. Evidently, the thus missing 20 percent must be replaced with new sand, that is with fresh sand which is not contaminated, not only in order to maintain a constant volume of sand but also to maintain the technological and forming characteristics which are expected of the casting sand.

As pointed out before, if the contaminant coating is brittle, for instance if it is formed by sodium silicate which was used as a binder for the same, the prior-art approach outlined above is fully usable for its intendedpurposes. However, if the currently predominantly used synthetic plastic resin binders are employed, then the contaminant coating which forms-on the spent casting sand will not be brittle but will be able to elastically yield in response to impact. That being the case, these contaminant coatings can be removed only partially or not at all by resort to the prior art, since they will not break on impact. The amount of re-usable spent sand which'can be thus obtained, that is which can be regenerated to the point where it can be used again, is too small to be of any value.

SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to overcome the disadvantages of the prior art.

More particularly, it is an object of the present invention to provide an improved method of regenerating casting sand even if the contaminant coating on the spent sand is of the non-brittle type.

Another object of the invention is toprovide an improved apparatus for carrying out the method.

In keeping with the above objects, and with others which will become apparent hereafter, one feature of the invention resides, in a method of regenerating casting sand, in the steps of admixing contaminant-coated spent casting sand with fresh uncontaminated casting sand, and subjecting the thus obtained mixture to mechanical agitation. During this agitation the fresh sand scours the contaminant coating off the spent sand and thus regeneratesthe sand.

It is advantageous if at least 10 percent by volume of fresh sand is admixed with the spent sand to be regenerated. The fresh sand can be admixed prior toregeneration, or during the regeneration itself.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a diagrammatic vertical section illustrating an embodiment of an apparatus for carrying out the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing the drawing in detail it will be seen that the FIGURE has a line A--A. That portion of the illustrated apparatus which is located above the line AA is in keeping with what is known from the prior art. The portion of the apparatus located below the line AA, except for the air inlet conduit 1, is new and, in conjunction with the portion above the line AA, provides for a novel apparatus according to the present invention.

The air inlet conduit 1 has air admitted into it by way of a non-illustrated source of supply, well known to those skilled in the art. The conduit 1 communicates with the opening 4a of a funnel-shaped hopper which accommodates spent contaminant-coated casting sand 3. A conduit section 6 has a lower open end located within the hopper 3, upwardly of the inlet 4a thereof, and it also has an upper open end which is located adjacent to but spaced from a stationary abutment baffle 5. The air entering through the conduit 1 into the inlet 4a entrains spent sand 3 and forms an air-sand mixture which is lifted upwardly in the conduit section 6 to impact against the baffle 5. The conduit section 6 is sur- Y 3 the hopper 3a is indicated by the arrow at the left-hand side of the drawing.

In accordance with the present invention there is provided an additional hopper 2a which is located downwardly of the hopper 3a and which has an inlet 4b which also communicates with the conduit 1. A portion 3b of the hopper 3a extends downwardly beyond the inlet 4a to form with the lower end of the hopper 2a the inlet 4b. The hopper 2a accommodates new uncontaminated casting sand 2, and the addition of further new uncontaminated casting sand into the hopper 2a is identified by the arrow at the left-hand side of the drawing.

In accordance with the present invention the air entering the conduit 1 in the direction indicated by the arrow first entrains new sand 2 which is advanced upwardly through the portion 3b and becomes admixed in the inlet 4a with spent 3, with the mixture of spent and new sand being advanced upwardly through the conduit section 6 to impact the abutment baffle 5. The admixture of new sand to spent sand is in a regulatable ratio, in accordance with the dimensions a and b shown in the drawing.

While in the apparatus according to the prior art, that is the portion located above the line AA in the drawing, the agitation and regeneration of the spent sand takes place only as the latter abuts the abutment baffle 5, in the apparatus according to the present invention the agitation and regeneration begins as soon as the new sand 2 contacts the spent sand 3 in the inlet 4a. The reason for this is that the new sand 2 will have already been accelerated in the portion 3b and will tangentially impact the grains of spent sand 3 in the inlet 4a, with the new sand 2 at this time having a velocity v and the grains of spent sand in the inlet 40 at this time having a velocity of v Since the new sand has sharp edges and impacts the articles of old sand, it creates turbulence and causes these particles of spent sand to turn, so that the mechanical agitation and regeneration already begins in the zone a and continues during the entire travel of the mixture of spent sand, new sand and air through the conduit section 6 until abutment with the baffle 5.

It will be appreciated therefore, that in the zone c the new sand undergoes its acceleration to reach the velocity at which it impacts the spent sand in the'inlet 4a.

In the prior art the spent sand has a minimum moisture content of 1.5 percent. By resort to the present invention this moisture content can be further decreased, because the new sand is always supplied in dried condition and becomes homogenously admixed with the spent sand during travel through the conduit section 6. This means that, related to the total volume of sand, a reduction in the moisture takes place. The homogenous admixture of spent sand and new sand, which takes place very early in the apparatus according to the present invention, namely rapidly after contact of the new sand with the spent sand, further affords the advantage that the time required for the subsequent final mixing is reduced and a more uniform admixture of the subsequently obtained mixture of new and regenerated sand with the binder material can be obtained.

The new quartz sand which is used for casting purposes has usually a quartz structure which has sharp edges and which during frictional contact with the contaminant-coated spent sand tends to scour the contaminant coating off the spent sand even if the contaminant coating has the basis of synthetic plastic resin binder and is therefore resilient, rather than being brittle. The admixture of the new sand with the spent sand thus results in a scouring-off of the contaminant coating, although it should be clearly understood that if the spent sand wereagitated by itself (without the admixture of the new sand) such a scouring action would not take place because the contaminant coating on the spent sand does not have the sharp edges as the new sand.

It is advantageous if the quantity of new sand admixed with the spent sand is at least 10 percent by volume of the spent sand, and it can of course be higher. By appropriately selecting the ratio-of new to spent sand, a sand mixture is obtained which after rcgeneration can be immediately re-used for casting purposes.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in the regeneration of casting sand, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that. from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:

1. In a method of regenerating casting sand, the steps of subjecting contaminant-coated spent casting sand to mechanical agitation; accelerating fresh uncontaminated casting sand; and contacting the accelerated fresh casting sand with said spent casting sand so that said fresh and said spent casting sand are admixed and the contaminant coating on said spent casting sand is at least partially scoured off by said fresh casting sand.

2. A method as defined in claim 1, wherein the contacting step is performed prior to the agitating step.

3. A method as defined in claim 1, wherein the contacting step is performed substantially simultaneously 6. In an apparatus for regenerating casting sand, a combination comprising upright conduit means having an inlet at a lower region thereof for the introduction of pressurized gaseous fluid and an outlet at an upper region thereof; first admitting means at a level of said conduit means equal to at least the level of said inlet for the admission of fresh uncontaminated casting sand into said conduit means so as to permit entrainment of said fresh casting sand by said gaseous fluid; second admitting means intermediate said first admitting means and said outlet for the admission of spent contaminantcoated casting sand into said conduit means so as to permit entrainment of said spent casting sand by said gaseous fluid and an at least partial scouring off of the contaminant coating on said spent casting sand by said fresh casting sand; and impact baffle means adjacent said outlet for impaction of the entrained fresh and spent casting sand so as to permit mechanical agitation ter. 

1. In a method of regenerating casting sand, the steps of subjecting contaminant-coated spent casting sand to mechanical agitation; accelerating fresh uncontaminated casting sand; and contacting the accelerated fresh casting sand with said spent casting sand so that said fresh and said spent casting sand are admixed and the contaminant coating on said spent casting sand is at least partially scoured off by said fresh casting sand.
 2. A method as defined in claim 1, wherein the contacting step is performed prior to the agitating step.
 3. A method as defined in claim 1, wherein the contacting step is performed substantially simultaneously with the agitating step.
 4. A method as defined in claim 1, wherein at least 10 percent of said fresh sand is admixed with said spent sand.
 5. A method as defined in claim 1, wherein the accelerating step comprises entraining said fresh sand in a stream of gaseous fluid and the contacting step comprises entraining said spent sand in said stream of gaseous fluid; and wherein said mechanical agitation comprises impacting the entrained sand against an obstacle.
 6. In an apparatus for regenerating casting sand, a combination comprising upright conduit means having an inlet at a lower region thereof for the introduction of pressurized gaseous fluid and an outlet at an upper region thereof; first admitting means at a level of said conduit means equal to at least the level of said inlet for the admission of fresh uncontaminated casting sand into said conduit means so as to permit entrainment of said fresh casting sand by said gaseous fluid; second admitting means intermediate said first admitting means and said outlet for the admission of spent contaminant-coated casting sand into said conduit means so as to permit entrainment of said spent casting sand by said gaseous fluid and an at least partial scouring off of the contaminant coating on said spent casting sand by said fresh casting sand; and impact baffle means adjacent said outlet for impaction of the entrained fresh and spent casting sand so as to permit mechanical agitation of said fresh and said spent casting sand.
 7. A combination as defined in claim 6, wherein said first and second admitting means each comprise a funnel surrounding said conduit means and communicating with the interior of the latter via a respective aperture.
 8. A combination as defined in claim 6, wherein said first and second means are so arranged relative to one another that said fresh sand has a higher speed than the admitted spent sand at the time of contact with the latter. 